The present invention relates to an ink jet printing head for effecting recording by ejecting liquid droplets, more particularly to an ink jet printing head, an ink jet head cartridge and ink jet printing apparatus using electrothermal transducer elements as ejection energy generating elements.
The ink jet recording technique is advantageous in that the noise is low, that the recording speed is high, that the recording is possible on so-called plain paper, not a heat sensitive paper, and that color recording is possible by ejecting different color inks. However, in order to provide a sharp and clear color recording particularly on plain paper, the following problems remain.
It is difficult to suppress color mixture (so-called bleeding) at a boundary between different colors with sufficient recording density maintained, on the plain paper. In order for the characters or lines to be sharply and clearly formed on the plain paper, an ink comprising approx. 20% by weight of diethylene glycol, approx. 3% by weight of ethanol, approx. 3% by weight of dye, and the remaining part of water is used. If such an ink is used, the dots formed on the plain paper by the ejected liquid droplets are sharp at the edges and are of high density, if there are no color boundaries between adjacent different color portions.
However, such an ink normally exhibits low penetrating speed into the recording material and slow drying after deposition on the recording material, and therefore, if different color dots are formed adjacent to each other, the above-described bleeding occurs with the result of remarkably unclear recording. The tendency increases with increase of color printing speed. And therefore, it is highly desired that these problems are solved particularly in the case of high speed color recording.
The inventors have carried out repeated tests using yellow, magenta, cyan and black (Y, M, C, Bk) and plain paper, under the condition of 360 dpi (dots per inch). It has been found that the above-described problem can be solved by reducing the quantities of the inks other than black inks, as compared with the black ink.
Among ink jet recording systems, an ink jet printing system using thermal energy and a bubble created thereby in the ink, is suitable for high density nozzle arrangement. However, the change of the volume of the ejected liquid is small even if the energy is supplied to an electrothermal transducer element (heat generating resistor), and therefore, it is practically not possible to significantly change the volume of the ejected liquid by changing supplied energy. For this reason, in order to change the ejected volume of the ink in the ink jet printing system using thermal energy, the area of the heater or a cross-sectional area of the ejection outlet is changed to change the ejected volume of the ink.
The configuration of the heater has been determined so that the ratio of the length and the width of the heater is substantially constant, in consideration of the energy using-efficiency for ink ejection. For example, if it is assumed that the volumes of ejections of black, magenta, cyan and yellow inks are 80 pl, 50 pl and 40 pl, the black ink nozzle has an ejection area of 1000 xcexcm2, and a heater size of 30xc3x97150 xcexcm; the magenta and cyan nozzles have an ejection area of 640 xcexcm2 and a heater size of 24xc3x97120 xcexcm; and the yellow nozzle has an ejection outlet area of 500 xcexcm2 and a heater size of 21xc3x97105 xcexcm. It has been found that these sizes are satisfactory.
However, if it is assumed that the electric pulse width of the voltage applied to the heater is preferably 3 xcexcsec, the voltage applied to the black heater is 28 V, and the voltages applied to the magenta and cyan heaters are 22 V, and the voltage applied to the yellow heater is 20 V, and therefore, the applied conditions have to be changed, and therefore, a plurality of voltages and a plurality of the voltage application circuits have to be provided in the main assembly.
The reason for this is as follows. Even if an attempt is made to use the same electric signal applying condition, the nozzle for the black ink does not eject the ink with the application voltage condition for the nozzle of the yellow heater, and if the applied voltage condition for the black ink heater is used for the yellow, magenta or cyan ink heater, the heater is subjected to thermal overload with the result of remarkably small durability. If another attempt is made to apply 20 V to the respective heaters and to adjust the amount of the applied energy to the heater by the pulse width, the pulse width for the black ink heater has to be significantly increased to 6 xcexcsec, for example. This is not preferable for the stability of the ink ejection or the like. As a result, a plurality of voltage application circuits for supplying different pulse widths are required. The use of a plurality of circuits increases costs.
Accordingly, it is a principal object of the present invention to provide a small size and low cost ink jet print head and ink jet cartridge which is easy to manufacture and wherein the volume of the ejected ink can be significantly changed even if the same electric signal is applied.
It is another object of the present invention to provide an ink jet printing head and an ink jet cartridge with which ink can be ejected in a proper manner by application of the same electric signal even if it comprises ink jet heaters having different configurations.
It is a further object of the present invention to provide an ink jet printing head, an ink jet cartridge and an ink jet printing apparatus, wherein the problems of the cost increase and complication due to the necessity for the plurality of voltage application circuits to eject different volumes of the ink, are solved.
According to an aspect of the present invention, there is provided an ink jet printing head for effecting printing by ejection of ink, comprising: a first electrothermal transducer having a heat generating resistor with a first area and wiring electrically connected with said heat generating resistor; a second electrothermal transducer having a second heat generating resistor with an area which is different from the area of said first heat generating resistor; wherein bubbles are produced in ink materials upon application of electric signals to said electrothermal transducers, by which different volumes of ink materials are ejected; wherein said first and second electrothermal transducers have substantially the same bubble production threshold voltage.
According to another aspect of the present invention, there is provided an ink jet printing head for effecting printing by ejection of ink, comprising: a first electrothermal transducer having a heat generating resistor with a first area and wiring electrically connected with said heat generating resistor; a second electrothermal transducer having a second heat generating resistor with an area which is different from the area of said first heat generating resistor; wherein bubbles are produced in ink materials upon application of electric signals to said electrothermal transducers, by which different volumes of ink materials are ejected; wherein lengths of said heat generating resistors measured in a direction of wiring, are substantially the same.
According to a further aspect of the present invention, there is provided an ink jet printing head for effecting printing by ejection of ink, comprising: a first electrothermal transducer having a heat generating resistor with a first area and wiring electrically connected with said heat generating resistor: a second electrothermal transducer having a second heat generating resistor with an area which is different from the area of said first heat generating resistor; wherein bubbles are produced in ink materials upon application of electric signals to said electrothermal transducers, by which different volumes of ink materials are ejected; wherein thicknesses of passivation films covering said first and second heat generating resistors are different.
According to a yet further aspect of the present invention, there is provided an ink jet head cartridge having the printing head and the ink container defined above, and an ink jet apparatus usable with the printing head defined above.
According to the present invention, the heaters have different areas so that the volumes of the ink ejected are made different depending on the colors, by which the bleeding can be decreased, while the manufacturing is easy. In addition, the size of the ink jet printing apparatus is small.
According to the present invention, the heaters having different dimensions have the same bubble-creating threshold electric pulse, so that only one kind of voltage application circuit is satisfactory, and therefore, the cost can be significantly reduced. In addition, the apparatus is simplified, and the size thereof is reduced.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.